The GALAH survey: a catalogue of carbon-enhanced stars and CEMP candidates

TL;DR

This paper utilizes GALAH survey spectra to identify and analyze a large sample of carbon-enhanced stars, including CEMP candidates, revealing their population characteristics and variability.

Contribution

It presents a new catalog of 918 carbon-enhanced stars and 28 CEMP candidates identified through spectral analysis, expanding the understanding of these stars in the galaxy.

Findings

Identified 918 carbon-enhanced stars, including 12 known in literature.

Found 28 CEMP star candidates among the sample.

Detected variability and Lithium enhancement in a subset of stars.

Abstract

Swan bands - characteristic molecular absorption features of the C$_2$ molecule - are a spectroscopic signature of carbon-enhanced stars. They can also be used to identify carbon-enhanced metal-poor (CEMP) stars. The GALAH (GALactic Archaeology with Hermes) is a magnitude-limited survey of stars producing high-resolution, high signal-to-noise spectra. We used 627,708 GALAH spectra to search for carbon-enhanced stars with a supervised and unsupervised classification algorithm, relying on the imprint of the Swan bands. We identified 918 carbon-enhanced stars, including 12 already described in the literature. An unbiased selection function of the GALAH survey allows us to perform a population study of carbon-enhanced stars. Most of them are giants, out of which we find 28 CEMP candidates. A large fraction of our carbon-enhanced stars with repeated observations show variation in radial velocity, hinting that there is a large fraction of variables among them. 32 of the detected stars also show strong Lithium enhancement in their spectra.